Device and method for automatically inspecting objects traveling in an essentially monolayer flow

ABSTRACT

A device and a method for automatically inspecting objects traveling in an essentially monolayer flow. The device comprises a detection unit through which the object flow passes, consisting of the following: elements for applying electromagnetic radiation in the direction of the plane of conveyance of the objects and defining a lighting plane, the intersection of the lighting plane and plane of conveyance defining a detection line; a receiver device periodically scanning each point on the detection line and receiving radiation reflected by an elementary measuring zone, the plane defined by the detection line and the optical input center being known as the scanning plane; elements for transmitting the reflected radiation. The radiation emitted is concentrated in the region of the lighting plane and the lighting plane and the scanning plane merge, whereupon the joint plane is inclined in relation to the normal of the plane of conveyance.

BACKGROUND OF THE INVENTION

The present invention relates to the characterisation and optionally theautomatic sorting of objects, in particular recyclable domesticpackagings, by their constituent materials and/or by their colour, thecombination of a material or of a constituent substance and of a colourhereinafter being called a category.

It relates to a device and a method for automatically inspectingtravelling objects with characterisation and discrimination according totheir chemical composition.

The machine according to the invention is particularly but notexclusively suitable for inspection purposes and optionally for sorting,at high speed, various recyclable plastics packagings, in particularbottles made of PET, HDPE, PVC, PP and PS, as well as paper/cardboard,composite (drink packs) or metal packagings.

However, this machine may also be used for inspecting and discriminatingany other objects or articles containing organic chemical compounds andtravelling with a substantially single layer planar presentation suchas, for example, fruits (discrimination by sugar content), anddiscrimination may be carried out on the basis of a major or minorchemical compound or of a plurality of chemical compounds.

In addition, said discrimination may end with separation of the flow ofobjects by sorting in categories or merely with counting andcharacterisation of said flow.

There are already numerous machines and numerous methods of theaforementioned type, in particular for sorting packagings according totheir constituent material.

However, these known machines all have fairly serious drawbacks andsignificant limitations.

Therefore, the sorting of domestic packagings is still largely manual atpresent, particularly in European countries where sorting by material isdemanded by the authorities responsible for recycling but also in othercountries.

Significant automation of sorting has recently taken place in Germany,but in a very particular context, at least with respect to plasticsmaterials. Sorting criteria do not concern the material but the shape(films, hollow bodies, or various mixed plastics). These existingmachines therefore sort a “mixed plastics” category frompapers/cardboards, after aeraulic presorting of the films and manualpresorting of hollow bodies. Machines for the sorting of compositepackagings or metal packagings are also found.

Existing machines differ greatly in terms of efficacy, depending on thetype of mechanical preparation of the flow of objects to be sorted.Three main solutions may be distinguished:

-   -   complete individualisation with a single object per receptacle,        without grasping an object;    -   a thread-form flow, the objects being aligned one behind the        other;    -   a planar flow, the objects being spread in bulk over a mat which        is much larger than their largest dimension and being        distributed in a single layer.

Only the last solution has proven suitable, from the points of view ofefficacy and productivity, for products which are as heterogeneous asrefuse, in particular domestic refuse. In fact:

-   -   Complete individualisation has never been industrially proven.        The prototypes developed with this type of presentation all        ceased operating afterwards.    -   The thread-type flow already existed in industrial over-sorting        machines in which the main flow was uniform and over-sorting        involved removing a small percentage of undesirable objects.        Applied to a heterogeneous flow of packagings, these thread-type        systems operated on particularly clean flows. However, these        machines have a limited throughput and necessitate the presence        of manual operators upstream of the machine to remove objects        likely to disturb operation, in particular large sheets of        plastic and large containers. Therefore, they do not constitute        a satisfactory solution for automation of sorting and have had        little success.    -   Planar flows, on the other hand, have proven themselves as this        is exactly the presentation of objects found in manual sorting.        It is thus known how to carry it out simply in the context of        domestic refuse, and the machines using this type of flow are        suitable for bulk sorting conditions and have met with much        greater success than the two other aforementioned types.

Only planar flow sorting, involving the currently most effectivemachines, will therefore be discussed hereinafter.

The document EP-A-0 706 838 in the name of the Applicant presents asorting machine and method suitable for objects in a planar flow. Thismachine uses at least one artificial vision system to locate the objectsand to recognise their shape and their colour, a robotic arm to graspand handle the objects and at least one complementary sensor torecognise their constituent material. This complementary sensor isadvantageously an infrared spectrometer.

This system has the advantage of being basically a multimaterial systemsince the main packagings are sorted by material and/or by colour andare distributed in a plurality of suitable containers. The same machinemay therefore sort up to eight different categories. Furthermore, theindividual gripping of the objects guarantees an excellent quality ofsorting, typically one error per 1,000 sorted objects.

However, the sorting rate of this system is limited by the individualgripping of the sorted objects and does not exceed 60 to 100 kg/h persorting module. The only way to increase this rate is to cascade aplurality of identical sorting modules, and this increases the overallbulk of the machine and its cost.

The document U.S. Pat. No. 5,260,576 presents a planar sorting machinewhich emits overhead the flow of electromagnetic radiation received bytransmission below the flow of objects. The intensity of this radiationenables the materials to be distinguished according to their relativeopacity in transmission. Thus, if the radiation consists of X-rays, thisdocument mentions satisfactory separation of PVC which contains an atomof chlorine which is opaque to X-rays, in comparison with the otherplastics which do not contain any, in particular PET. Depending on theresult, a row of nozzles will or will not eject one of the classes ofobjects downwards.

However, this detection principle is too basic for complex cases: allobjects have a degree of opacity, and it will be appreciated thatmultiple thicknesses of a material which is only slightly opaque (forexample PET/polyethylene terephthalate) may not be distinguished from asingle thickness of a more opaque different material (for example,PVC—polyvinyl chloride). There is therefore the risk of ejecting allthese sparingly opaque objects at once in error. In addition, thissystem can only distinguish PVC from other plastics: it is incapable ofdistinguishing PET from HDPE (high density polyethylene) or PAN(polyacylonitrile). Existing machines according to this document havelimited efficacy and low outputs (proportions of desired objects fromamong the ejected objects): of 10 to 30%. Finally, a significantdrawback of the transmission assembly is that at least one of the twoelements, the sensor or the transmitter, has to be below the flow. Thereis therefore a risk of recurrent soiling or blockage of the lowerelement, necessitating repeated interventions at relatively shortintervals.

The document EP-A-0 776 257 describes a planar sorting machine which hasa high throughput and is capable of recognising one material from aplurality of materials. The material to be recognised is selected at thetime of construction of the machine by appropriate fixed calibration.

In this machine, mere infrared lighting is emitted overhead and thesensor is also placed on top, so it analyses the light which isscattered back vertically by the objects.

Reception is effected via a plane or semicircular concave mirrorextending over the entire width of the mat, then by a polygonal rotatingmirror. The point of measurement is therefore scanned cyclically overthe entire width of the mat.

The light received from the measuring point is then divided by anassembly of semi-reflective mirrors in a plurality of flows. Each flowpasses through an interferential filter centred over a specificwavelength, then ends at a detector. Each detector therefore measuresthe proportion of received light contained in the bandwidth of thefilter. Analysis of the relative intensities measured by the variousdetectors allows a decision as to whether the material present at thepoint of measurement is or is not the desired material. The number offilters mentioned in this document is between 3 and 6.

The presence of a large-sized mirror of this type constitutes a fragilepoint of the overall structure, elongates the detection/ejectiondistance, increases the overall bulk of the detection station and islikely to lead to distortion and introduce inhomogeneities in the lightflux recovered for analysis, leading to errors of detection.

In such architecture, the speed of detection is the main issue: thereare 25 to 50 measuring zones per line, and 100 to 150 lines have to beanalysed per second in view of the speed of circulation of the flow. Themagnitude is therefore 5,000 measurements/s. Such a speed involvessignificant constraints:

-   -   the detection algorithm must be sufficiently simple (therefore        few operations and simple processing) to be carried out in real        time;    -   the reception electronics must be very fast;    -   the quantity of light received must be sufficient in a very        short time.

The detection algorithm has to carry out two-dimensional reconstitutionof the objects to be sorted before proceeding to eject them, and thisnecessitates a relatively large distance between the detection zone andthe ejection zone, increasing the risks of erroneous ejection owing to amovement of the objects between detection and ejection.

The aforementioned problem concerning the quantity of light is criticaland explains why the machine according to this document can onlyrecognise a predefined material:

-   -   multimaterial recognition would necessitate the use of at least        8 to 16 wavelength ranges (or PLO) and not just 3 to 6 ranges;    -   in addition, the widths of the PLOs, which are relatively large        in the example mentioned (32 to 114 nm) would have to be reduced        in a range of 5 to 20 nm since a larger number of PLOs has to be        distinguished in the same spectral width.

The two effects are added together: the greatest number of PLOs woulddivide the quantity of light received by each filter by approximately 3;the reduced width of each PLO means that each filter would allow afraction, which is about 5 times smaller, of the received light to passthrough. To maintain the same level of signal, the lighting powerrequired for the machine would therefore pass from one to 3×5=15 kW.Such a power would not be realistic (cost, energy consumption, heating).

The document WO 99/26734 presents a planar sorting machine having a highthroughput, with architecture which is fairly close to the previousdocument but discloses multimaterial recognition.

To achieve this, this document approaches the problem of the quantity oflight differently: it proposes a vision system upstream on the conveyorof infrared detection, this system being quite comparable to the onementioned in the aforementioned document EP-A-0 706 838. This systemallows each object present to be located and, in the region of infrareddetection, allows a single measuring point which follows the travellingobject to be controlled by a set of position-sensitive mirrors. Theanalysis time available becomes relatively long, of the order of 3 to 10ms, as a single point is analysed per object. Implementation, althoughnot specified, may therefore use known technology which is compatiblewith this analysis time. For example, a spectrometer with a bank ofphotodetectors (typically 256 components, each corresponding to awavelength) with resolution of 4 to 6 nm per detector may be used.

However, this solution also has several drawbacks:

-   -   it necessitates additional material, namely a vision system;    -   it is dependent on the selection by vision of the point of        spectrometric measurement on the object, and this may be awkward        in the presence of labels or soiling;    -   it is dependent on the immobility of the object on the mat: as        the two detections are made on zones of about 1 m×1 m, the        object moves by at least 1 m between its detection by vision and        its detection by spectrometry, then by 0.5 m on average between        its detection by spectrometry and its final ejection. Immobility        is never ensured when the conveyor advances at 2.5 m/s,        particularly if the objects are bottles which are likely to        roll.

The machine described in this document is obviously more flexible butmore expensive and much less effective than the previous one.

Finally, the document DE-A-1 96 09 916 describes a miniaturisedspectrometer for a planar plastics sorting machine operating with adiffraction grating to spread the infrared spectrum over an output stripand a small number of sensors corresponding to wavelengths which areunevenly distributed in this output strip. It is mentioned in thisdocument that 10 well-selected sensors rather than the 256 sensors of aconventional bank of photodiodes may suffice. However, each of these 10sensors has an area equivalent to each sensor of a bank, in other wordstypically a rectangle of 30×250 μm². A surface of this type gatherslittle light and limits the speed of analysis to 200 measurements persecond. Therefore, a spectrometer of this type cannot analyse all thepoints of a high-speed conveyor with the above-mentioned speeds andresolutions.

This last document therefore proposes the production of a line ofidentical parallel microspectrometers for analysing a planar flow.According to the inventor, the cost of a spectrometer would be minimisedby microsystem production techniques, but the necessary resolutioninvolves 25 to 50 spectrometers on the line to cover the width of theconveyor mat: the total cost, like the maintenance constraints, aretherefore very high. In addition, few details are provided in thisdocument on the production of such a machine, and there does not seem tobe any machine of this type currently in operation.

In addition to the drawbacks and limitations inherent in each of theabove-mentioned devices and methods, one major drawback which is commonto all these devices and methods should be mentioned, namely theirinability to reliably process objects having a significant height, forexample of about 10 to 30 cm, owing to the inadequate intensity ofapplied radiation at this distance from the plane of conveyance Pc ofthe travelling objects, or owing to the inability to recover theradiation to be analysed or else for both the aforementioned reasons.

SUMMARY OF THE INVENTION

Thus, the main object of the present invention is to propose a machineand a method for inspecting and optionally sorting, which operates witha high through-put and for substantially single-layered flows ofobjects, this machine and this method being capable of discriminatingreliably between objects having significant heights while being simpleand economical to construct and use.

In addition, the invention should dispense with an independent visionsystem to locate the objects, minimise the number of sensors required,maintain good reliability, particularly in the event of sorting, whenthe objects move relative to the support transporting them and haveoptimised efficacy in exploitation of the emitted radiation.

The invention accordingly relates to a machine for automaticallyinspecting objects travelling substantially in a single layer on or overa plane of conveyance of a conveyor, for discriminating between theseobjects by their chemical composition, this machine comprising at leastone detection station through or beneath which the flow of objectspasses, this detection station comprising, in particular:

-   -   means for applying electromagnetic radiation in the direction of        the plane of conveyance, emitting said radiation so as to define        a lighting plane, the intersection of said lighting plane and        said plane of conveyance defining a detection line extending        transversely to the direction of travel of the objects for the        width of the conveyance,    -   a receiver device periodically scanning each point on said        detection line and receiving, all the time, radiation reflected        by an elementary measuring zone located in the region of the        point scanned at this instant, the plane defined by said        detection line and the optical input centre of said device being        known as the scanning plane,    -   means for transmitting to at least one analysis device said        radiation reflected in the region of the scanning elementary        measuring zone,        the machine being characterised in that the emitted radiation is        concentrated in the region of the lighting plane and in that        said lighting plane and the scanning plane coincide, the common        plane being inclined to the perpendicular to the plane of        conveyance.

These dispositions allow maximum application of radiation in theexploited zone for the acquisition and systematic correspondence of theilluminated zone and of the analysed zone, whatever the height of theobjects in a range of heights defined by the dimensions of the machineand the sensitivity of the acquisition and analysis means.

Thus, the superimposition of the lighting and scanning (detection)planes gives a good depth of field and the inclination thereof to theplane of the analysed objects effectively eliminates the parasitic lightformed by the specular reflection.

According to a preferred embodiment of the invention, the receiverdevice comprises a moving reflective member comprising or carrying theoptical input centre, directly receiving the radiation reflected in theregion of the scanning elementary measuring zone and having dimensionswhich are substantially equal to the dimensions of said elementarymeasuring zone which it displaces, preferably substantially greater.

Advantageously, the application means consist of broad spectrum lightingmeans, the applied radiation consisting of a mixture of electromagneticradiation in the visible range and in the infrared range and saidlighting means comprise members which concentrate the emitted radiationin the region of the plane of conveyance on a transverse detection stripperiodically scanned by the elementary measuring zone and of which thelongitudinal median axis corresponds to the detection line.

The use of broad spectrum lighting, for example of the halogen type, andof wavelengths of between 1,000 and 2,000 nm (for each emission point)allows chemical analysis of the objects disposed on the conveyor.

In order to even out the lighting of the detection zone, the means forapplication of radiation preferably consist of two mutually spacedapplication units disposed in an alignment which is transverse to thedirection of travel of the objects, each unit comprising an elongateemission member combined with a member in the form of a profiledreflector of elliptical section.

According to a characteristic of the invention, each elongate emissionmember is positioned substantially in the region of the near focus ofthe elliptical reflector associated therewith, the means for applyingradiation being positioned and the reflectors being shaped anddimensioned in such a way that the second, remote focus is located at adistance from the plane of conveyance substantially corresponding to themean height of the objects to be sorted.

This lighting may therefore be focused on a large range of depths(typically about 200 mm).

The light intensity in the region of the detection zone, in particularin the region of its extreme portions, may optionally be furtherincreased in that walls reflecting the radiation emitted by theapplication means are disposed along the lateral edges of the conveyor(for example, conveyor mat or belt), in particular in the region of theends of the detection strip, and extend horizontally and vertically,substantially to the height of said application means.

According to a preferred variation of the invention, the receiver deviceis in the form of a receiver head located at a distance above the planeof conveyance and comprising or carrying, on the one hand, a movingreflective member in the form of a plane mirror (of which the geometriccentre advantageously substantially coincides with the optical inletcentre), disposed substantially centrally relative to the plane ofconveyance of the conveyor and oscillating by pivoting with a rangewhich is sufficient for the moving elementary measuring zone to explorethe entire detection strip during a half-oscillation and, on the otherhand, a focusing means, for example in the form of a lens, for thefraction of radiation reflected by an elementary portion of thedetection strip and transmitted by the oscillating mirror in thedirection of said means, said head also comprising or carrying the endwhich has the inlet orifice of the means for transmitting said fractionof radiation, after it has been focused by the means, toward at leastone spectral analysis device.

The moving elementary measuring zone which progressively scans theentire surface of the travelling conveying support is defined, incombination, by the characteristics of the inlet orifice of thetransmission means and the characteristics of the focusing means and bytheir relative disposition, the focusing means and the successivetransmission means being located outside the field of exploration of theoscillating mirror (defined by its optical or geometric centre) locatedin the scanning plane, the axis of alignment of the mirror/focusingmeans/inlet orifice being located in said plane containing said field.

The fraction of detection or measurement surface reflected by theoscillating mirror will advantageously be at least slightly greater inarea than the elementary measuring zone centred relative thereto and ofthe same or a different shape.

To achieve a compact structure, the oscillating plane mirror forming themoving reflective member may advantageously be located between the twounits forming the means for applying radiation and in a relativedisposition which is such that said units do not interfere with thefield of exploration of said mirror.

As mentioned hereinbefore, the scanning plane containing said field ofexploration and the plane containing the focuses of the ellipticalreflectors coincide and this coincidence of the illuminated zone andanalysed zone allows optimum consideration of the objects havingsignificant heights.

The mirror will preferably be located at a greater distance from theplane of conveyance than the units of application means, for example inthe form of halogen lamps, however, it may also be disposed at the sameheight or even closer to this plane than said units without affectingthe efficacy of the detection station.

According to a characteristic of the invention, the transmission meanspreferably consist of a bundle of optical fibres all or the majority ofwhich are connected to an analysis device which splits or breaks downthe reflected radiation into its various spectral components anddetermines the intensities of some of said components having wavelengthswhich are characteristic of the substances of the objects to be sorted,and of which a minority may advantageously be connected to an analysisdevice detecting the respective intensities of the three basic colours,said optical fibres having a square or rectangular section arrangementin the region of the inlet orifice.

According to a further advantageous characteristic of the invention, afirst analysis device consists, on the one hand, of a spectrometer witha diffraction grating which breaks down the multispectral light fluxreceived from the elementary measuring zone into its various constituentspectral components, in particular into the infrared range, on the otherhand, of means for recovering and transmitting the elementary lightfluxes corresponding to various unevenly spaced ranges of the spectrum,characterising the chemical substances and compounds of the objects tobe discriminated, for example in the form of separate bundles of opticalfibres and, finally, of photoelectric conversion means which deliver ananalogue signal for each of said elementary light fluxes.

The multispectral light flux originating from the elementary measuringzone is introduced into the spectrometer in the region of an inlet slotand the elementary light fluxes are recovered in the region of outletslots having a shape and dimensions identical to those of the inlet slotand positioned as a function of the dispersion factor and of the rangesof the spectrum to be recovered, the end portions for the egress of thefibres of the major component of the fibre bundle forming thetransmission means and the end portions for the ingress of the opticalfibres of the recovery and transmission means having identical lineararrangements and being mounted in the inlet slot and the outlet slotsrespectively.

To facilitate handling and installation of the recovery and transmissionmeans without the risk of damaging them, the end portions for ingress ofthe optical fibres of the bundles forming the recovery and transmissionmeans are mounted in thin plates provided with appropriate receivingrecesses preferably combined with holding and locking back-plates so asto form assembly and positioning supports for said optical fibres in thebody of the spectrometer.

Preferably, the body of the spectrometer comprises a rigid receiving andholding structure with locking for said supports, which enables them tobe positioned by sliding and to be installed by stacking, optionallywith insertion of appropriate shims so as to position said supports inthe locations corresponding to the impact zones of the elementary lightfluxes to be recorded.

An arrangement of this type allows rapid, easy and precise adaptation ofthe inspection machine for detecting different groups of materials,characterised by specific wavelength ranges which differ according tothe type of objects and the selectivity to be employed.

Consequently, the first spectral analysis device consists mainly of ameans for distributing the light without significant losses according toits constituent wavelengths and of a small number of detectors (10 to20) in the form of photoelectric conversion means having a high unitsurface area, each of the detectors being specific to a wavelength range(PLO), these PLOs conveniently being selected for robust simultaneousidentification of a plurality of substances or chemical compoundscorresponding, for example, to a plurality of materials.

In addition, a second analysis device which recognises the colour of theobjects is combined with the previous device and takes a small portionof the light flux from the fibre bundle and sends it toward threesensors which are each sensitive to one of the basic colours, in otherwords red, green or blue.

To coordinate and control the various devices, members and components ofthe machine, the machine also comprises a unit for processing andmanaging operation of the detection station such as a computercontrolling, in particular, the movement of the moving reflective memberand optionally of the conveyor, sequencing the acquisition of theradiation reflected in the region of the moving elementary measuringzone and processing and evaluating the signals transmitted by theanalysis devices, for example by comparison with programmed data, inorder to determine the chemical composition of each of the inspectedobjects or the presence of a chemical substance in said objects, bycorrelating the results of said determination with determination of thespatial location of said objects.

According to a particularly preferred variation of the invention, thedetection strip has the form of an elongate rectangular surface of smallwidth extending perpendicularly to the median axis and transversely overthe entire width of the plane of conveyance of the conveyor, for examplein the form of a mat or belt of which the upper surface coincides withsaid plane of conveyance.

Thus, in the context of application to the sorting of objects and for aconveyor in the form of a belt travelling at about 2.5 m/s, thedetection/discrimination distance may be limited to about 100 mm andthis minimises the probability of an unstabilised object on the matbeing displaced prior to discrimination thereof, which is manifested,for example, by the escape thereof.

The invention also relates to a machine for automatically sortingobjects according to their chemical composition, these objectstravelling substantially in a single layer on or over a conveyor, thissorting machine comprising an upstream detection station which isfunctionally coupled to a downstream station for active separation ofsaid objects as a function of the results of the measurements and/oranalyses effected by said detection station, characterised in that thedetection station is a detection station as described hereinbefore.

Advantageously, the detection station or its unit for processing andmanaging operation transmit actuating signals to a control module forthe ejection means in transverse alignment of the active separationstation as a function of the results of said analyses, a salvo ofactuating signals being emitted after each complete exploration of atransverse detection strip by the moving elementary measuring zone.

Preferably and to avoid, as far as possible, sorting errors due todisplacement of the objects relative to the conveyor between detectionand ejection, the detection line is located in the immediate vicinity of(for example at less than 30 cm from) the ejection means, for example bylifting, in the form of a row of nozzles which deliver jets of gas,preferably air.

The present invention also relates to a method for automaticallyinspecting objects travelling substantially in a single-layer over aplane of conveyance or surface of a conveyor, said method allowingdiscrimination between these objects by their chemical composition andinvolving:

-   -   passing the flow of objects to be inspected through or beneath        at least one detection station,    -   emitting electromagnetic radiation toward the plane of        conveyance via corresponding application means so as to define a        lighting plane, the intersection of said lighting plane and said        plane of conveyance defining a detection line extending        transversely to the direction of travel of the objects,    -   periodically scanning any point on said detection line via a        receiver device which receives, at any instant, the radiation        reflected by an elementary measuring zone located in the region        of the point scanned at this instant, the plane defined by said        section line and the optical input centre of said device being        known as the scanning plane,    -   transmitting said radiation reflected in the region of the        scanning elementary measuring zone to at least one analysis        device via appropriate transmission means,        the method being characterised in that the radiation emitted is        concentrated in the region of the lighting plane and in that        said lighting plane and the scanning plane are combined, the        common plane being inclined to the perpendicular to the plane of        conveyance.

According to an advantageous characteristic of the invention, saidmethod involves, in particular, concentrating the radiation, preferablyin the visible and infrared range, in the region of the plane ofconveyance on a transverse detection strip which is periodically scannedby the elementary measuring zone and of which the longitudinal medianaxis corresponds to the detection line, so as to obtain high intensityof radiation which is substantially uniform over the entire surface ofsaid detection strip.

More precisely, said method may involve sequentially scanning thedetection strip with the moving elementary measuring zone by pivotingoscillation of a plane mirror forming the reflective member, focusingthe light flux originating from the elementary measuring zone on theinlet orifice of the transmission means in the form of a bundle ofoptical fibres, bringing the majority of the captured multispectrallight flux toward the inlet slot of a spectrometer forming part of afirst means of analysis, breaking down this light flux into its variouselementary spectral components, recovering the light fluxes of some ofthese components corresponding to specific narrow wavelength ranges inthe region of outlet slots and transmitting them via appropriate meansto photoelectric conversion means in order to supply first measuringsignals, simultaneously to optionally bring a small portion of thecaptured multispectral light flux toward a second analysis meansdetermining the respective intensities of the three basic colours andsupplying second measuring signals, processing said first and optionallysecond measuring signals in the region of a computerised processing andmanagement unit, controlling, in particular, the movement of the movingreflective member, sequencing the acquisition of the radiation reflectedin the region of the moving elementary measuring zone and processing andevaluating the signals transmitted by the analysis devices by comparisonwith programmed data in order to determine the chemical composition ofeach of the inspected objects or the presence of a chemical substance insaid objects.

If the inspection method is used in a sorting machine as describedhereinbefore, it may also involve causing the processing and managementunit to transmit, as a function of the results of processing of themeasuring signals, actuating signals to a module for controllingejection means of a separation station located downstream of thedetection station relative to the flow of objects and, finally, ejectingor not ejecting each of the various objects travelling on the supportingplane of conveyance of the conveyor as a function of the transmittedactuating signals.

According to an additional preferred characteristic of the invention, asalvo of actuating signals is emitted on completion of each scanning ofthe detection strip and processing of the corresponding measuringsignals, taking into account the measuring signals of the previousscanning as the case may be.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood better by means of thefollowing description which refers to a preferred embodiment given as anon-limiting example and explained with reference to the accompanyingschematic drawings, in which:

FIG. 1A is a schematic view of an automatic inspection machine accordingto the invention;

FIG. 1B is a partial schematic view of an automatic sorting machineaccording to the invention equipped, in particular, with an upstreamdetection station and a downstream separation station;

FIG. 2 is a schematic lateral elevation showing the inclination of thelighting means and of the reflecting means of the receiver head formingpart of the detection station;

FIG. 3 is a partial transparent view in a direction opposed to thedirection of travel of the conveyor means, of some of the machines shownin FIG. 1;

FIG. 4A is a schematic view of the functional members of the receiverhead forming part of the machine according to the invention, and of theamplitude of the oscillations of the reflective member and the resultantscanning in the region of the detection zone;

FIGS. 4B to 4D show three positions of the moving elementary measuringzone during scanning of the detection zone;

FIGS. 5 and 6 are partially schematic and partially structural views ofthe recovery and transmission means and of the analysis devices;

FIG. 7 is a partial front elevation of the end portions for ingress ofthe recovery and transmission means mounted in the outlet slots of thespectrometer forming part of the first analysis device, and

FIG. 8 shows a detail of a particular assembly of two adjacent inlet endportions of the recovery and transmission means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in the figures of the accompanying drawings, and moreparticularly FIGS. 1 to 4, the machine for automatically inspectingobjects 2 comprises at least one detection station 4 through or beneathwhich the flow of objects 2 passes, this detection station 4 comprising,in particular:

-   -   means 6 for applying electromagnetic radiation in the direction        of the plane of conveyance Pc of the conveyor 3, emitting said        radiation so as to define a lighting plane Pe, the intersection        of said lighting plane Pe and said plane of conveyance Pc        defining a detection line 7 extending transversely to the        direction of travel of the objects 2,    -   a receiver device 8 periodically scanning each point on said        detection line 7 and receiving radiation reflected by an        elementary measuring zone 12 located in the region of the point        scanned at this instant, the plane defined by said detection        line 7 and the optical input centre 8″ of said device being        known as the scanning plane Pb,    -   means 10 for transmitting said radiation reflected in the region        of the scanning elementary measuring zone 12 to at least one        analysis device 11, 11′.

According to the invention the emitted radiation is concentrated in theregion of the lighting plane Pe and said lighting plane Pe and thescanning plane Pb coincide, the common plane Pe, Pb being inclined tothe perpendicular D to the plane of conveyance Pc. This last arrangementallows specular reflection, in particular, to be eliminated.

The term “transverse” in relation to the detection line 7 denotes anextension over the entire width of the plane of conveyance Pc defined bythe conveyor 3, preferably but not exclusively rectilinearly andperpendicularly to the direction of travel of the objects 2.

The plane of conveyance Pc, in the case of a planar conveying support,at the surface thereof and, in the case of non-planar supports, such aswheels mounted on chains (for individualised transport, for example forfruits) will correspond to a median plane characterising the travel ofsaid objects.

It will be appreciated that the following description corresponds to apractical, non-limiting, embodiment of a sorting machine containing aninspection machine according to the invention and explained withreference to the accompanying FIGS. 1 to 8.

It will also be appreciated that the detection station 4 is identical inthese two machines, the sorting machine also comprising a separationstation 5.

FIG. 1 shows the general structure of the machine 1 for automaticsorting by chemical composition or substance. The objects 2 travel athigh speed (2 to 3 m/s) onto a conveyance means or conveyor 3 so thatthey are substantially spread in a single layer. The surface of theconveyor 3 is dark and its constituent material (generally matt blackrubber) is selected so as to be different from the materials or chemicalcompounds to be recognised.

These objects 2 pass through a detection region defined in the area of adetection station 4. This region is substantially delimited by lightingmeans 6 having a broad (visible and infrared) spectrum, whichconcentrate the light flux via reflectors 6′ so as to markedlyilluminate a zone 7′ in the form of a narrow strip for effectivedetection, of which the width is 25 to 40 mm.

The zone 7′ is analysed at high speed using an oscillating mirror 8′which is controlled by a computer 23 and cyclically directs themeasurement toward each of the constituent elementary zones 12′ of thezone 7′. A complete scanning cycle of the zone 7′ takes approximately 8ms. During this period, the conveyor 3 has advanced by a distancesubstantially equal to the width of said zone 7′ so there is nodetection “hole”: every point of the conveyor 3 or of the travellingplane of conveyance Pc is analysed.

The light collected by the mirror 8′ is focused by a lens forming afocusing means 9 on the inlet orifice 10′ of a bundle 10 of opticalfibres 10″. The bundle 10 is subdivided into two portions: the firstportion brings the majority of the light flux to a spectrometer 14forming part of a first analysis device 11 and subdividing this portionof flux according to its constituent wavelengths in the near infraredrange (NIR). A small number n of suitably selected PLOs (wavelengthranges) is transmitted to a module containing conversion means 16 in theform of photodiodes NIR having a large unit surface area and to anamplification stage. This module converts the light signals into thesame number of analogue electrical signals which are then analysed bythe computer 23.

The second portion of the bundle 10 is brought to a second analysisdevice 11′ corresponding to a colour detection module. This moduleallows the red, green and blue components to be isolated by filtrationand then allows the light signals to be converted into electric signalsand to be amplified. After conversion, the output signals are alsoanalysed by the computer 23.

The computer 23 combines all the previous information so that categoriesof objects to be ejected or not ejected can be defined, and thuscontrols the separation station 5 and each of the ejection means 5′ inthe form of nozzles in a row, by means of a control module 24.

The blown objects 2′ end up in a receptacle 25 whereas the unblownobjects 2″ fall directly in front of this receptacle. Obviously, thisarrangement is not the only solution: the nozzles 5′ could just as wellbe placed above the conveyor 3 and thus blow down the objects 2′ to beseparated. This second configuration has advantages in certainapplications.

A first decisive advantage of the machine 1 is that the device forreceiving reflected light (mirror 8′ and lens 9′ assembly) does notextend physically over the entire width of the plane of conveyance Pccorresponding, for example, to the surface of a mat of a conveyor 3, butis a single device and is installed only in the centre of the medianline of the conveyor 3. This prevents unevenness between variousreceiving points, which would impair the uniformity of the signalthrough the detection zone 7′.

A second decisive advantage of the geometry of the machine 1 is that adetection zone is placed as close as possible to the row of ejectionnozzles 5′. The detection/ejection distance d may be limited byappropriate computing means, to about 100 mm, and this minimises theprobability of an unstabilised object on the mat being displaced priorto the ejection thereof. It is limited only by the software processingtime which is very fast as it relates to the information from a singleline of measurements, or possibly only two adjacent lines. This distanceis much smaller than the distance in the previously described knownplanar flux machines.

A person skilled in the art will note that such a small distance d doesnot allow two-dimensional analysis of each object prior to a decision:in the case of an elongate object such as a 300 mm long bottle, thedecision to actuate the nozzles 5′ on the leading end of the object mustbe taken before the trailing end of the same object has been completelyanalysed. However, this limitation does not significantly impairdetection or ejection.

Referring in particular to FIGS. 1, 2 and 3 of the accompanyingdrawings, the lighting means will now be described in more detail.

The desired aim is to bring a maximum of light onto the detection zone7′ with the constraint that the lamps must be sufficiently far removedfrom the circulating objects 2 to allow these objects to circulatewithout interference. Approximately 50 cm between lamps and mats isdesired. The amount of light is evaluated summarily in electric W/cm²,with reference to a halogen lamp of colour temperature 3400 K.

From among the various possible lighting technologies, a set ofstationary halogen lamps has been selected as this is the simplest, mostwidely used solution. Conventionally, however, industrial spotlightswhich significantly disperse the light are used.

The use of these commercial spotlights, even with a small angularaperture, necessitates many individual lamps and ends up with a lowdensity of lighting.

To overcome the drawbacks associated with these known means, theinventors have developed lighting based on fine halogen tubes 6′ asemission members which are aligned at the same height above the mat 3and associated with elliptical reflectors 6′. A reflector 6′ of thistype allows the light to be focused perfectly on the other focus F′ ifthe halogen tube 6″ is placed at one of its focuses F. To obtaindimensions compatible with the machine 1 in its practical embodiment,the ellipse should have the following parameters:

-   -   semi major axis a=300 to 400 mm    -   eccentricities e of about 85 to 92%.

Manufacture of the reflectors 6′ must be very precise for goodoperation, but it is easier than that of conventional reflectors withcircular symmetry such as parabolic mirrors. A developable surface whichmay be produced by folding is obtained in this case.

Preferably, the machine is assembled in such a way that F′ is placed afew centimeters above the conveyor mat 3 at a height (H) correspondingto the average thickness of the travelling objects (H=25 to 50 mm).

With an embodiment of the lighting means 6 as mentioned hereinbefore,the inventors have found that the best intensity distribution isobtained by using only two fairly long reflectors 6′ separated by avacuum, as shown in FIG. 3. In addition, to avoid losses of light at theends of the mat 3, vertical planar reflectors or reflective walls 13 and13′ are added at these ends, if necessary. These ends return the lighttoward the mat.

A simple, inexpensive, layout with a small number of lamps is thusobtained and all of the light is concentrated on a narrow strip to beanalysed: 800 mm×40 mm, containing the detection zone 7′ and centredthereon.

With two members of 100 electric W, the mean density obtained is2×1000/(80×4)≈6 W/cm², that is about 60 times greater than the daytimesun. Such a concentration is compatible only with a mat 3 which moves athigh speed to prevent the burning thereof. Electric safety devices areprovided to shut off the lighting automatically in the event of astoppage of said mat.

Referring now to FIGS. 1, 2 and 4 of the accompanying drawings, themeans 8, 9, 10 for reception and transmission of the light reflected inthe region of the detection zone 7′ will now be described in moredetail.

The object is to analyse approximately 40 to 80 elementary surfaceswithin the zone 7′ using a moving elementary measuring zone 12. Theseelementary surfaces 12′ have a rectangular shape with dimensions of10×20 to 20×20 mm. Such an elementary surface 12′ will hereinafter becalled a “pixel”, all of said pixels corresponding to the detection zone7′.

To minimise the number of sensors required, the inventors have selecteda moving assembly which sequentially scans all the pixels. A singlesensor therefore allows all the measurements, providing that measurementis carried out very rapidly.

The preferred solution is an oscillating mirror 8′, 30 mm in diameter,which is mounted in a detection head 8 and oscillates with an angularamplitude c between the positions shown in FIG. 4A. Depending on theinstantaneous angle delta (FIG. 4C), it returns the light from a pixel12′ toward the fixed lens 9 which focuses it in a bundle 10 of opticalfibres 10″. The pixel 12′ has been shown as a dot so that FIG. 4 will belegible.

The number of measurements per second is obtained as a function of thespeed of travel of the mat 3 and the selected pixel size. Thus, forexample, with a pixel of 20 mm×20 mm, there are 40 measurements per lineover a width of 800 mm. With a speed of travel of 2.5 m/s, there are 125lines of 20 mm in width per second: 125×40=5000 measurements/second aretherefore found. For geometric reasons, moreover, only half anoscillating alternation may be exploited. The duration of an individualmeasurement may therefore be 1(5000×2)=10⁻⁴ sec=100 μs.

In view of this scanning, non-vertical angles of return of light areaccepted. A sufficiently large height of the mirror 8′ must therefore beselected to limit the angle b of the field of exploration C to a valueof just below 60°. Experience has shown that the geometric aiming errorsare acceptable for these angles. As any variation in angle α of arotating mirror is manifested by a variation of 2.α in the position ofthe reflected beam, the plane mirror can therefore oscillate over halfan angle, or 30° in total.

The lens 9 is disposed as far as possible below the mirror 8′ withoutinterfering with the field of exploration C (angle b). It should not betoo low above the conveying mat 3 either.

The design of the lighting with an empty space in the centre above themat 3 is utilised to make the plane of oscillation of scanning Pb of themirror 8′ (comprising the field of exploration C) coincide with thelighting plane Pe (plane containing the focuses F and F′) and passingthrough the median axis of the detection zone 7′. With suitably selecteddimensions and arrangement, the measuring zone (angle b) does notinterfere with the tubes 6″ or the reflectors 6′.

This design is very advantageous for analysing objects 2 of significantheight (up to 200 mm high) because, whatever the height of the object,the illuminated zone and the analysed zone coincide.

Although the lighting and the measuring spot are no longer focused ifthe surface of the object moves away from the point F′, detection isreliable despite a reduction in the definition of the pixel, because thelight intensity remains substantially identical. In fact, the lightingis dispersed well over a larger area but, at the same time, the objectapproaches the halogen tube and therefore receives a greater directflux, and the distance between the mirror and object decreases, and thisincreases the density received on the mirror 8′.

In the designs of the known non-coplanar devices, the lighting has to bedispersed over a large angle to effectively light a high object, and theavailable intensity is reduced by the same amount.

To prevent the specular rays which lack information from being takeninto consideration in the recovered reflected light flux, the commonplane (lighting plane Pe and scanning plane Pb) of the lighting means 6and the oscillating mirror 8′ is inclined at an angle alpha relative tothe perpendicular to the plane of conveyance Pc. It can thus be seenthat there is an angle gamma between the closest specular ray and theaxis of the sensor (axis comprising mirror 8′/lens 9/orifice 10′). Thisangle gamma must be at least 5°, preferably greater than 10° for highsecurity (see FIG. 2 of the accompanying drawings).

Conversely, an excessive inclination alpha would reduce the quantity ofuseful light collected by the sensor. A good compromise seems to be anangle alpha of about 20°.

The lens 9 serves to limit the size of the analysed pixel 12′, even at agreat distance from the conveying mat 3.

It gives a clear image of the analysed pixel 12′ at the inlet orifice10′ of the fibre bundle 10, providing that the end of the correspondingbundle at the orifice 10′ is placed slightly downstream of the focaldistance upstream of the lens 9. The magnification, in other words theratio between the size of the pixel 12′ and the size of the inlet 10′ ofthe bundle 10 is equal to the ratio of the distances to the lens.

Under these conditions, the collected light flux is optimal. In fact, itcan be shown mathematically that it is almost independent of thedistance between the mirror and conveyor and that it is identical to theflux collected by a fibre bundle having the same surface area placed inthe vicinity of the conveyor and under the same lighting and without anoptical system.

The aforementioned existing single-material machines utilise 3 to 6suitably selected PLOs. A PLO is defined by the value of a centralwavelength and by a spectral width. For example, the PLO centred at 1420nm and with a width of 20 nm is the range of all the wavelengths between1410 and 1430 nm. The use of 3 to 6 PLOs is effectively sufficient todistinguish a given product from all the others. Experience has shownthat it is insufficient to simultaneously recognise the range ofmaterials commonly found in refuse, namely:

-   -   the main plastics materials: PET, PVC, PE, PS, PP, PAN, PEN;    -   so-called “engineered” plastics: ABS, PMMA, PA6, PA6.6, PU, PC;    -   food packs (Tetrapaks), cardboards, of which the cellulose is        detected;    -   the other products, without a spectral signature: metals and        glass.        Various technologies may be used to separate the PLOs:    -   interferential filters,    -   AOTFs (acousto optic tunable filters),    -   diffraction grating.

The inventors adopted the third solution as it is tried-and-tested andis free from physical movements and has a very good light output: from60 to 90% in the spectrum which is of interest here.

The following description refers to FIGS. 5 and 6 of the accompanyingdrawings.

In a diffraction grating, the light is dispersed through the outlet slotin the manner of a rainbow, depending on the wavelengths. The grating ischaracterised by a dispersion, which is the ratio between the changes ofwavelengths expressed in nm, and the distance over the outlet slot,expressed in mm. For good resolution of analysis, the inventors haveselected a dispersion of between 20 nm/mm and 30 nm/mm.

The bundle of optical fibres 10 allows the reflected light received fromthe pixel 12′ to be conveyed (multispectral light flux 14″) from thesquare section end comprising the orifice 10′ (having a shape identicalto the pixel) to the inlet slot 17 of the spectrometer 14 where thefibres are rearranged in a fine vertical slot 17′.

The image of the inlet slot 17 for each PLO selected at the outlet ofthe grating 14′ is a slot 17′ of the same shape and dimensions as at theinlet. The various elementary light fluxes 14′″ corresponding to thevarious PLOs are collected by the outlet slots 17′. A grating of fibrebundles 15′ forming reception and transmission means 15 is provided inthis region, and these fibres are rearranged at the other end in circles15″, each of which is fixed to the contact of a photodiode 16 made ofInGaAs having an approximate active surface area of 1 mm².

Advantageously, the spectral width of the PLOs is fixed and is about 5nm, and this allows the use of identical photodiodes. However, bundles15 of different sections combined with photodiodes 16 having acorresponding surface area (for example a spectral width of 10 nm withtwo rows of attached optical fibres in the case of a photodiode surfacearea of approximately 2 mm²) may also be constructed. Therefore, thereceived light flux may be increased or the resolution refined, asdesired.

Owing to the above-described assembly, the amount of light is dividedonly once: if the number of outlet bundles is doubled, each of them willhave as much light as in the original assembly.

It is very advantageous that the construction of the machine 1 accordingto the invention allows the choice of the PLOs to be easily changed tooptimise the search for new products which will appear on the market infuture.

The design adopted and shown in FIGS. 7 and 8 allows great flexibilityfor modifying the selected PLOs, provided that the number of them isfixed. The following technological solutions allows easy modification ofassembly:

-   -   the fibre bundles 15 are provided with precision-machined        rectangular ferrules produced in two parts 18 and 19. It is        therefore easy to handle them without breaking them. A ferrule        of this type is formed from a first plate 18 with a recess 18′        containing and blocking the ends of the optical fibres 15′ and        closed by a back plate 19.    -   the minimum spacing between the ferrules defines the resolution        of the system (FIG. 8), in other words the minimum deviation        between two PLOs: it is determined by the size of these        ferrules. In the extreme case, the protective plate or back        plate 19 of one of the two ferrules may be eliminated, and this        gives a wavelength deviation of 10 nm (FIG. 8).    -   a set of shims 22 machined with high precision (tolerance of        about +/−0.15 μm) is used to select arbitrary positioning of the        ferrules in the outlet zone of the grating 14′. For example, a        shim of 5000 μm and a shim of 280 μm result in a spacing of 5280        μm.    -   all the ferrules 18, 19 and the shims 22 are stacked in a        support 20 fixed in a rectangular holding box 21 of appropriate        shape.

Rearrangement of the PLOs therefore involves simply removing ferrules18, 19 and shims 22 from the holding box 21 then replacing certain shimswith shims of different dimensions, and finally replacing them in thebox. Operation is simple, quick (a single operating session) andreversible.

The photodiodes of the conversion means 16 provide an intensity which isproportional to the number of photons incident on all their surface fora given period. This current is converted into voltage and amplifiedbefore being delivered to the computer 23.

The amplification means may comprise an integrating element which makesthe final signal level proportional to the exposure time. A plurality ofequivalent methods are possible:

-   -   a simple RC (resistance—capacitance) filter of which the time        constant is adjusted so as to be about half the measuring time;    -   a charge transfer device (CCD) which empties a        charge-accumulating capacitance at regular intervals;    -   a summation module which calculates an integral implanted in        software after digital conversion.

The inventors preferred the first method, which is the simplest and theleast restrictive for the computerised processing system 23.

The active surface of the photodiodes 16 used actually determines theentire design of the recovery/transmission/analysis assembly. In fact,it is not worth producing an outlet bundle 15 form the diffractiongrating 14′ which is greater than the surface of the associated diode16: the additional surface would not be utilised. Similarly, the laws ofoptics mean that the dimensions of the inlet slot 17 of the grating 14′are the same as the dimensions of the outlet slot 17′. The bundle ofoptical fibres 10 obviously keeps the active surface unchanged, in otherwords about 1 mm². Finally, as stated hereinbefore, the flux received atthe end of the inlet orifice 10′ of this bundle depends only on itssurface area and on the intensity of lighting in the region of the planeof conveyance Pc (for example surface of the mat of a conveyor 3),subject to suitable dimensioning of the optical system 8′ and 9.

The outcome of the foregoing is that the final signal level forsubstance analysis is proportional only to the following variables:

-   -   the illuminated surface of the photodiode;    -   the intensity of lighting on the conveyor mat;    -   the spectral width of the PLO used;    -   the exposure time for each measurement.

Thus, an analysis system which is much faster but also much finer thancould be produced with a bar-type spectrometer is obtained by maximisingthe intensity of lighting, by maintaining narrow PLOs and by usingsensors (photodiodes) having a large illuminated surface area.

FIG. 5, in combination with FIG. 1, shows a possible embodiment of thesecond analysis device 11′ (colour analysis).

This second device 11′ could also be produced using a diffractiongrating.

In the visible range, however, the wavelength selectivity does not haveto be very fine. Bandwidths of 60 nm are quite sufficient. In addition,there is no issue of flexibility as the three basic colours are fixed inthe perception of the human eye: therefore, the PLOs never change.Rather than using a diffraction grating, therefore, it is simpler andmore cost effective to use coloured filters which may be placed in frontof each receiving diode. These are the 26R, 26V, 26B filters shown,which are specific to red, green and blue respectively.

The photodiodes 27 associated with the aforementioned filters are madeof silicon and cover the entire visible range: this material is veryinexpensive and has very good detectivity, about 100 times greater thanInGaAs in the infrared range. Owing to this high sensitivity, it is notworth bringing a bundle of fibres in front of the diode: a single fibrehaving a diameter of 200 μm gives an adequate signal.

It is therefore sufficient to take three optical fibres from the bundle10 for use in colour detection. The end comprising the inlet orifice 10′may therefore comprise about 20 fibres, of which 16 or 17 are located atthe end penetrating the inlet slot 17 of the spectrometer 14 and ofwhich three penetrate the analysis device 11′ or colour module. In viewof the amount of visible light available, it is also possible to use asingle fibre for the colour and to distribute its light over threefilters: the maximum sensitive surface area is therefore left for theportion of the bundle 10 connected to the spectrometer 14.

After the silicon photodiodes 27, a conventional amplification stage,not shown, allows the analogue signals to be brought to a level which issufficient to collect them in the computer 23.

The invention is obviously not limited to the embodiment described andshown in the accompanying drawings. Modifications are possible, inparticular with regard to the constitution of the various elements or bysubstitution of technical equivalents without departing from the scopeof protection of the invention.

1. Machine for automatically inspecting objects travelling substantiallyin a single layer on or over a plane of conveyance of a conveyor, fordiscriminating between these objects by their chemical composition, saidmachine comprising at least one detection station through or beneathwhich the flow of objects passes, said detection station comprising:means for applying electromagnetic radiation in the direction of theplane of conveyance, emitting said radiation so as to define a lightingplane, the intersection of said lighting plane and said plane ofconveyance defining a lighting line extending transversely to thedirection of travel of the objects, a receiver device periodicallyscanning each point on said lighting line and receiving radiationreflected by an elementary measuring zone located in the region of thepoint scanned at this instant, the plane defined by said lighting lineand the optical input centre of said device being known as the detectionplane, means for transmitting to at least one analysis device saidradiation reflected in the region of the scanning elementary measuringzone, wherein the emitted radiation is concentrated in the region of thelighting plane and wherein said lighting plane and the detection planecoincide as a common plane being inclined to the perpendicular to theplane of conveyance.
 2. Machine according to claim 1, characterised inthat the receiver device (8) comprises a moving reflective member (8′)carrying the optical input centre (8″), directly receiving the radiationreflected in the region of the scanning elementary measuring zone (12)and having dimensions which are substantially equal to the dimensions ofsaid elementary measuring zone (12) which it displaces, preferablysubstantially greater.
 3. Machine according to claim 1, characterised inthat the application means consist of broad spectrum lighting means, theapplied radiation consisting of a mixture of electromagnetic radiationin the visible range and in the infrared range and in that said lightingmeans comprise members which concentrate the emitted radiation in theregion of the plane of conveyance on a transverse detection strip (7′)periodically scanned by the elementary measuring zone and of which thelongitudinal median axis corresponds to the lighting line.
 4. Machineaccording to claim 1, characterised in that the means (6) forapplication of radiation consist of two mutually spaced applicationunits disposed in an alignment which is transverse to the direction oftravel of the objects (2), each unit comprising an elongate emissionmember (6″) combined with a member (6′) in the form of a profiledreflector of elliptical section.
 5. Machine according to claim 4,characterised in that each elongate emission member (6″) is positionedsubstantially in the region of the near focus (F) of the reflector (6′)associated therewith, the means for applying radiation (6) beingpositioned and the reflectors (6′) being shaped and dimensioned in sucha way that the second, remote focus (F′) is located at a distance fromthe plane of conveyance (3) substantially corresponding to the meanheight (H) of the objects (2) to be sorted, said focuses (F, F′) beinglocated in the lighting plane (Pe).
 6. Machine according to claim 3,characterised in that walls (13, 13′) reflecting the radiation emittedby the application means (6) are disposed along the lateral edges of theconveyor (3), in particular in the region of the ends of the detectionstrip (7′), and extend horizontally and vertically, substantially to theheight of said application means (6).
 7. Machine according to claim 3,characterised in that the receiver device (8) is in the form of areceiver head carrying, on the one hand, a moving reflective member (8′)in the form of a plane mirror disposed substantially centrally relativeto the plane of conveyance (Pc) of the conveyor (3) and oscillating bypivoting with a range which is sufficient for the moving elementarymeasuring zone (12) to explore the entire detection strip (7′) during ahalf-oscillation and, on the other hand, a means (9) for focusing thefraction of radiation reflected by an elementary portion of thedetection strip (7′) and transmitted by the oscillating mirror (8′) inthe direction of said means (9), said head (8) also carrying the endwhich has the inlet orifice (10′) of the means (10) for transmittingsaid fraction of radiation, after it has been focused by the means (9),toward at least one spectral analysis device (11, 11′).
 8. Machineaccording to claim 7, characterised in that the focusing means (9) andthe successive transmission means (10) are located outside the field ofexploration (C) of the oscillating mirror (8′) located in the scanningplane (Pb), the axis of alignment of the mirror (8′)/focusing means(9)/inlet orifice (10′) being located in said scanning plane (Pb). 9.Machine according to claim 7, characterised in that the oscillatingplane mirror forming the moving reflective member (8′) is locatedbetween the two units forming the means for applying radiation (6) andin a relative disposition which is such that said units do not interferewith the field of exploration (C) of said mirror (8′).
 10. Machineaccording to claim 1, characterised in that the transmission means (10)consist of a bundle of optical fibres (10″) all or the majority of whichare connected to an analysis device (11) which breaks down the reflectedradiation into its various spectral components and determines theintensities of some of said components having wavelengths which arecharacteristic of the substances of the objects to be sorted, saidoptical fibres (10″) having a square or rectangular section arrangementin the region of the inlet orifice (10′).
 11. Machine according to claim10, characterised in that a minority of the optical fibres (10″) of thebeam (10) is connected to an analysis device (11′) which detects therespective intensities of the three basic colours.
 12. Machine accordingto claim 10, characterised in that the analysis device (11) consists, onthe one hand, of a spectrometer (14) with a diffraction grating (14′)which breaks down the multispectral light flux (14″) received from theelementary measuring zone (12) into its various constituent spectralcomponents, in particular into the infrared range, on the other hand, ofmeans (15) for recovering and transmitting the elementary light fluxes(14′″) corresponding to various unevenly spaced ranges of the spectrum,characterising the chemical substances and compounds of the objects (2)to be discriminated, for example in the form of separate bundles ofoptical fibres and, finally, of photoelectric conversion means (16)which deliver an analogue signal for each of said elementary lightfluxes (14′″).
 13. Machine according to claim 12, characterised in thatthe multispectral light flux (14″) is introduced into the spectrometer(14) in the region of an inlet slot (17) and in that the elementarylight fluxes (14′″) are recovered in the region of outlet slots (17′)having a shape and dimensions identical to those of the inlet slot andpositioned as a function of the dispersion factor and of the ranges ofthe spectrum to be recovered, the end portions for the egress of thefibres (10″) of the major component of the fibre bundle forming thetransmission means (10) and the end portions for the ingress of theoptical fibres (15′) of the recovery and transmission means (15) havingidentical linear arrangements and being mounted in the inlet slot (17)and the outlet slots (17′) respectively.
 14. Machine according to claim13, characterised in that the end portions for ingress of the opticalfibres (15′) of the bundles forming the recovery and transmission means(15) are mounted in thin plates (18) provided with appropriate receivingrecesses (18′) preferably combined with holding and locking back-plates(19) so as to form assembly and positioning supports (20) for saidoptical fibres (15′) in the body of the spectrometer (14).
 15. Machineaccording to claim 14, characterised in that the body of thespectrometer (14) comprises a rigid receiving and holding structure (21)with locking for said supports (20), which enables them to be positionedby sliding and to be installed by stacking, optionally with insertion ofappropriate shims (22) so as to position said supports (20) in thelocations corresponding to the impact zones of the elementary lightfluxes (14′″) to be recorded.
 16. Machine according to claim 3,characterised in that it also comprises a unit (23) for processing andmanaging operation of the detection station (4) such as a computercontrolling, in particular, the movement of the moving reflective member(8′) and optionally of the conveyor (3), sequencing the acquisition ofthe radiation reflected in the region of the moving elementary measuringzone (12) and processing and evaluating the signals transmitted by theanalysis devices (11, 11′), for example by comparison with programmeddata, in order to determine the chemical composition of each of theinspected objects (2) or the presence of a chemical substance in saidobjects (2), by correlating the results of said determination withdetermination of the spatial location of said objects (2) as the casemay be.
 17. Machine according to claim 16, characterised in that thedetection strip (7′) has the form of an elongate rectangular surface ofsmall width extending perpendicularly to the median axis andtransversely over the entire width of the plane of conveyance (Pc) ofthe conveyor (3).
 18. Machine for automatically sorting objectsaccording to their chemical composition, these objects travellingsubstantially in a single layer on a conveyor, this sorting machinecomprising an upstream detection station which is functionally coupledto a downstream station for active separation of said objects as afunction of the results of the measurements and/or analyses effected bysaid detection station, characterised in that the detection station (4)is a detection station according to claim
 1. 19. Sorting machineaccording to claim 18, characterised in that the detection station (4)or its unit (23) for processing and managing operation transmitactuating signals to a control module (24) for the ejection means (5′)in transverse alignment of the active separation station (5) as afunction of the results of said analyses, a salvo of actuating signalsbeing emitted after each complete exploration of a transverse detectionstrip (7′) by the moving elementary measuring zone (12).
 20. Sortingmachine according to claim 18, characterised in that the detection line(7) is located in the immediate vicinity of, for example at less than 30cm from the ejection means (5′), for example by lifting, in the form ofa row of nozzles which deliver jets of gas, preferably air.
 21. Methodfor automatically inspecting objects travelling substantially in asingle-layer on or over a plane of conveyance of a conveyor, said methodallowing discrimination between said objects by their chemicalcomposition and comprising: passing the flow of objects to be inspectedthrough or beneath at least one detection station, emittingelectromagnetic radiation toward the plane of conveyance viacorresponding application means so as to define a lighting plane, theintersection of said lighting plane and said plane of conveyancedefining a lighting line extending transversely to the direction oftravel of the objects, periodically scanning any point on said lightingline via a receiver device which receives, at any instant, the radiationreflected by an elementary measuring zone located in the region of thepoint scanned at this instant, the plane defined by said lighting lineand the optical input centre of said device being known as the detectionplane, transmitting said radiation reflected in the region of thescanning elementary measuring zone to at least one analysis device viaappropriate transmission means, wherein the radiation emitted isconcentrated in the region of the lighting plane and wherein saidlighting plane and the detection plane are combined as a common planebeing inclined to the perpendicular to the plane of conveyance. 22.Method according to claim 21, characterised in that it involvesconcentrating the radiation, preferably in the visible and infraredrange, in the region of the plane of conveyance on a transversedetection strip which is periodically scanned by the elementarymeasuring zone and of which the longitudinal median axis corresponds tothe lighting line, so as to obtain high intensity of radiation which issubstantially uniform over the entire surface of said detection strip.23. Method according to claim 21, characterised in that it involvessequentially scanning the detection strip (7′) with the movingelementary measuring zone (12) by pivoting oscillation of a plane mirrorforming the reflective member (8′), focusing the light flux originatingfrom the elementary measuring zone (12) on the inlet orifice (10′) ofthe transmission means (10) in the form of a bundle of optical fibres(10″), bringing the majority of the captured multispectral light flux(14″) toward the inlet slot (17) of a spectrometer (14) forming part ofa first means of analysis (11), breaking down this light flux (14″) intoits various elementary spectral components (14′″), recovering the lightfluxes of some of these components corresponding to specific narrowwavelength ranges in the region of outlet slots (17′) and transmittingthem via appropriate means (15) to photoelectric conversion means (16)in order to supply first measuring signals, simultaneously to bring, asthe case may be, a small portion of the captured multispectral lightflux (14″) toward a second analysis means (11′) determining therespective intensities of the three basic colours and supplying secondmeasuring signals, processing said first and optionally second measuringsignals in the region of a computerised processing and management unit(23) controlling, in particular, the movement of the moving reflectivemember (8′), sequencing the acquisition of the radiation reflected inthe region of the moving elementary measuring zone (12) and processingand evaluating the signals transmitted by the analysis devices (11, 11′)by comparison with programmed data in order to determine the chemicalcomposition of each of the inspected objects (2) or the presence of achemical substance in said objects (2).
 24. Method according to claim23, characterised in that it involves causing the unit (23) to transmit,as a function of the results of processing of the measuring signals,actuating signals to a module (24) for controlling ejection means (5′)of a separation station (5′) located downstream of the detection station(4) relative to the flow of objects (2) and, finally, ejecting or notejecting each of the various objects (2) travelling on the supportingplane of conveyance (Pc) of the conveyor (3) as a function of thetransmitted actuating signals.
 25. Method according to claim 24,characterised in that a salvo of actuating signals is emitted oncompletion of each scanning of the detection strip (7′) and processingof the corresponding measuring signals, taking into account themeasuring signals of the previous scanning as the case may be.